With the current thrust for more fuel efficient and low emission vehicles, many novel solutions for internal combustion engine architectures and operating strategies have been developed. One such strategy is to simply shut off the engine when the engine is operating in an idle mode. Many configurations have been proposed to effect a quick restart of the engine. The simplest and most cost effective systems incorporate a traditional or “off the shelf” starter/pinion gear and flywheel/ring gear configuration. As such, this type of start-stop strategy has minimal impact on engine and transmission architectures compared to other hybrid strategies. The response time of this system may be lengthy, which is an important consideration as automakers try to deliver seamless vehicle restart and launch. The time required to energize the traditional power relay switching and the drive gear engagement mechanisms of the starter account for a significant fraction of the total delay time.
This delay time can be better understood by way of explanation of the operation of a traditional starting system. The typical starter controls found in a vehicle today have the starting contacts contained within a key operated ignition switch. However, a pedal operated ignition switch may be employed for a “mild hybrid” configuration. When the ignition key is turned against spring pressure from the “on” position to the “start” position, the starting contacts close. This in turn connects a starter motor solenoid to the vehicle battery. A solenoid is required since the starter motor needs a massive feed of electrical current from the battery to set its internal components working.
Upon connection, coils contained within the solenoid become energized producing a magnetic field that pulls an armature inward. This armature engages a pinion actuator at one end, which in turn shuttles a pinion gear mounted to the starter motor shaft to engage the ring gear of the engine's flywheel. Located behind the pinion gear is a coil spring that will ensure that the pinion gear meshes with the flywheel ring gear in the event the gear teeth do not mesh properly in a condition referred to as “butting”. Simultaneously, the armature movement forces a heavy switch to connect the starter motor to the battery and engine cranking will begin. The coils within the solenoid are of a sufficient magnetic strength to simultaneously shuttle the pinion gear and close the starter motor switch. A spring on the pinion actuator pulls the pinion out of mesh when the current to the solenoid is interrupted upon engine start. Although this method requires a lag time of only seconds, a more responsive method is desirable to ensure seamless operation of a start-stop “mild hybrid”.